1. Field of the Invention
The present invention relates to the oxidation of bituminous materials especially for the preparation of high grade asphaltic materials particularly suited for use in paving and roofing applications.
2. Prior Art
Historically, paving grade asphalts were produced by the refiner by various methods or combinations of methods such as atmospheric distillation of crude oil with subsequent vacuum distillation to obtain the desired asphaltic product. Another method is air blowing, with or without an oxidation catalyst, a soft vacuum tower residual at 350.degree. to 550.degree. F. (177.degree. to 288.degree. C.) either by a batch method or continuous in line oxidation to the desired product specification. Another method is to solvent precipitate a soft vacuum tower residual to product specifications; and still another method is to solvent precipitate a soft vacuum tower residual to a low penetration hard asphalt followed by back blending with a softer vacuum bottoms to achieve the proper specification characteristics.
All of the aforementioned methods can be used singularly or in combination to produce high quality asphaltic products. The choice of methods, in reality, is dependent upon the crude type. This invention is concerned with the above processes where air blowing in the presence of a finely ground (comminuted) oxidation catalyst is employed. We have discovered that by using a much smaller percentage of the finely ground catalyst of the present invention, the "blowing curve" of the asphalt flux can be altered to produce a product having a higher penetration at a given softening point and in remarkably shorter time. As can be appreciated, both of these attributes are of considerable economic value.
In the past, bituminous materials, particularly asphalt materials, have been treated by passing an oxidizing gas through the bituminous materials in a molten condition. The effect of the conventional type of air blowing is to partially oxidize the asphalt in a manner resulting in decreasing penetration and increasing viscosity and softening point. To promote the oxidation process, oxidizing catalysts have been utilized in the past. U.S. Pat. No. 1,782,186 states that the chloride, carbonate and sulfate salts of zinc, iron, copper or antimony can be used as catalyst in air blowing petroleum residuals to asphaltic materials. U.S. Pat. No. 1,782,186 exemplifies only the use of the chloride salt. Also, U.S. Pat. Nos. 2,179,208 and 2,287,511 describe processes for making asphalt. In all of the examples of the '208 and '511 patents, residium is first air blown and then "polymerized" using halides of certain metals as catalysts. These two patents list other catalyst possibilities, including sodium carbonate. U.S. Pat. No. 3,440,073 to Loren M. Fowler and Harry D. Hurrell, discloses a method for deodorizing asphalt for use as sealants in refrigerators and freezers wherein air and steam are blown through molten asphalt flux to which has been added a small or minor quantity of a water solution of one or more water-soluble inorganic alkaline materials, such as sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate. The primary purpose of said treatment is to deodorize asphalt for special applications. Other patents of relevance to this invention are U.S. Pat. Nos. 2,370,007 to Donald E. Carr; 2,421,421 to Arnold J. Hoiberg; and 3,126,329 to Jean Fort.
Penetration by definition is the consistency of a bituminous material expressed as the distance in tenths of a millimeter that a standard needle vertically penetrates a sample of material under known conditions of loading, time, and temperature. In essence, the penetration of a bituminous material is synonymous with viscosity at the temperature specified.
Viscosity may simply be defined as the measure of the resistance to flow of a liquid in the presence of a force. It has been shown desirable in asphalts such as paving asphalts to have a high penetration at a given viscosity. For example, an asphalt pavement constructed with asphalt cement having a penetration (ASTM D5) of 40, viscosity (ASTM D2171) at 140.degree. F. (60.degree. C.) of 2000 poises, and a viscosity (ASTM D2171) at 275.degree. F. (135.degree. C.) of 300 centistokes would not perform as well as the same asphalt having the same viscosities but a penetration of 60. The 40 penetration asphalt at lower temperatures (below 77.degree. F. (25.degree. C.)) would become brittle and break up under repeated traffic load. In other words, the 40 penetration asphalt at 77.degree. F. (25.degree. C.) is more susceptible to changes in temperature.
One object of this invention is to catalytically produce a paving grade asphalt which is less susceptible to changes in temperature. Another object of this invention is to reduce the oxidation time. Another object of this invention is to reduce the quantity of catalyst required. Another object of this invention is to provide an improved process for producing said asphalt. Still another object of this invention is to provide an improved and novel paving grade asphalt product.
Roofing asphalts are markedly different from paving asphalts. The air blowing process is frequently employed to manufacture certain paving grade asphalts; however, all roofing asphalts are manufactured by the air blowing process. One very important similarity exists between paving grade asphalts and roofing asphalts, i.e., a higher penetration at a given softening point is desirable. In other words, it is desirable to produce a roofing asphalt which is less susceptible to temperature change. Roofing manufacturers have historically used softening point which, in essence, is another method to designate viscosity.
Some roofing fluxes (roofing asphalt precursors) can be air blown to specifications without the use of a catalyst. Some require a catalyst. The use or non-use of a catalyst usually depends on the type of crude from which the roofing flux is derived. Refiners and asphalt roofing manufacturers have historically utilized Lewis acid catalysts such as halides of iron, aluminum, copper, tin, zinc, antimony, as well as phosphorus pentoxide in the production of roofing grade asphalts. Ferric chloride and phosphorous pentoxide are presently the most commonly used catalysts. These catalysts work quite well except they are very corrosive, and the amount of maintenance required on storage tanks, fume burners, pumps, etc. amounts to millions of dollars annually. In addition, the Lewis acid catalyzed asphalts deterioriate cellulosic-based products, such as roofing felts, spreading mops, etc., which are used during the manufacturing and application processes.
One of the objects of this invention is to catalytically produce a novel roofing asphalt which is less susceptible to changes in temperature. Another object of this invention is to reduce processing costs, and increase operating capacity by reducing the time for air blowing a roofing flux to roofing asphalt specification requirements. The reduction in total oxidation time is associated with the accelerated catalytic initiation of the oxidation reaction causing a pronounced exotherm. Another object of this invention is to reduce the amount of catalyst required. Another object of this invention is to greatly reduce maintenance costs by utilizing a new non-corrosive, inexpensive, readily available catalyst. A further object of this invention is to provide a roofing asphalt which does not deteriorate cellulosics used in the roofing manufacturing and application processes. It is also an object of this invention to achieve an end product improvement over roofing asphalts produced by conventional catalysts known to the art such as ferric chloride, phosphorous pentoxide, etc. Another object of this invention is to produce, by catalysis, a novel, improved roofing material from a bituminous material which, when subjected to the normal non-catalytic air blowing process produces inferior roofing asphalts. Another object of this invention is to produce, by catalysis, a superior asphaltic roofing material exceeding specifications from a bituminous material which, when subjected to the normal non-catalytic air blowing process, produces only acceptable quality roofing asphalt. Another object of this invention is to provide improved catalytic processes for producing said asphalt.
Further objects of this invention will be apparent to the skilled artisan from the Summary and Detailed Description of the Invention, hereinbelow.